Rail flaw detector mechanism



H. C. DRAKE RAIL FLAW DETECTOR NIECHANIQSMI Filed Dec. l5, 1958 Flai. A l 6 fir-1&4.

f ATTORNEY A l 245741965' 46012' R41/L Pntente'd June 4,1940

UNITED ASTATES PATENT oFFlcE Sperry Products, Inc., l poration of New York Hoboken, N. J., a cor- Applicatlon December 15, 1938, Serial No. 245,827 14 Claims. (Cl. 175-183) This invention relates to the art j ,of rail ilaw detection, although the term rail is 'used merely for the purpose of convenience and it will be found that the invention is applicable also to the testing of electrical conductors generally. The invention is particularly adapted for -use on the Sperry rail flaw detector car which is now Well known and which is disclosed, for example, in my Patent No. 2,133,687, granted October 18, lo. 1938. As therein illustrated, the detector` mechanism is mounted on.a rail car which moves along the rails and has facilities for continuously setting up an electromagnetic field surrounding the rail, which-field will` be uniform except in the region of flaw. When a flaw is encountered the iield is distorted and such distortion is detected by ilux responsive means which preferably take the form of a pair of opposed induction coils. Said coils normally cut a constant number n of lines of force but in the region of flaw they cut successively different numbers of lines of force to generate an E. vWhich after being suitably amplified, as shown in said patent, may be caused to operate suitable indicators such as a pen on a moving chart within the car and a paint gun forv spraying paint on the rails in the region of flaw.

The present invention relates to an improvement in-the said detector mechanism which improvement resides in the design of the detector coils. By means of my improved design I obtain more eflicient detection than was heretoforeL possible. The theory and construction of said coils will be more fully described inthe following specification. l

In the accompanying drawing, Fig. 1 is aperspective view, largely diagrammatic, showing a portion of a rail with detector coils embodying my invention cooperating therewith.

Figs. 2 and 3 are side elevations of rails with diagrammatic representations of the theory underlying my invention.

Fig. 4 is a vertical section through a'rail and a diagrammatic representation of the flux distribution surrounding the same. I Fig. 5 is a plotv showing the 4distribution of ilux density with respect to the distance above the rail-head.

Referring first to Fig. 2, there is shown a rail 'R having an internal fissure F indicated in dotted lines. In accordance with the construction of the- Sperry rail flaw-detector car described in the lintroduction, current is passed through a portion of said rail successively from a generator G within the car to spaced brushes I2 and I3' in sliding engagement with the rail to establish an elecv tromagnetic field surrounding the same. The said eld will be 'uniform except in the region of flaw. where it will be distorted. Agraph 20 the region aiected by flaw witha circular coil but with drawn above the rail R indicates the ilux intensity at various points along the rail and it will be seen that said flux intensity is constant until F is reached when it will be seen that the flux intensity diminishes. The extent of the region of ux distortion depends upon the size of the flaw. Thus, for instance, a fissure, that is, a fissure occupying 10% of the areaof the rail-head, will cause a distortion for a distance longitudinally of the rail about as shown in Figs. 2 and 3, that is, for about 21/2 inches. A very large fissure such as a 40% fissure may cause a distortion for a distance longitudinal of the rail of as much as six inches. In the Sperry detector system the region of flaw is detected by means of tion coils arranged in tandem so that first one and then the other of the coils enters the region of flaw to set up a differential E. M. F. which after being suitably amplied by amplifier A may operate recording mechanism as hereinbefor'e described. For this purpose Ihave indicated aA pair of opposed detector coils I5 and I6. l

Heretofore these coils took a circular form 'with many windings arranged spool-like on a core. The axis of the coll was positioned laterally with respect to have found that the best results are obtained not coils having the shape disclosed in Fig. 1, that is, rectangular coils whose horizontal or longitudinal dimension is greatly in excess of the vertical dimension so that the effect is long, flat coils lying close to the surface of the rail. The theory underlying the improved performance of such detector coils can best be explained by reference to the diagram, Figs. 2 to 5 inclusive. In Fig. 2 it will be seen that if a coil, such as coil 2|, has a longitudinal dimension which is less than one-half of the length of the distorted region set up by flaw F, in other words, which is less than the distance 22, then the maximum output of coil 2| is not obtained. This is apparent because it will be seen that when the rear edge the region of distortion, the induced E. M. F. therein is opposed to the induced E. M. F. in the leading edge 24 so that the maximum generated E. M. F. of coil 2| is represented by the distance 25 on graph 20. If, however, a coil such as 3| is employed which has a dimension of -the rail equal to at least half of the distortion caused by flaw F, then the maximum differential E. M. F. generated by said coil is represented by the distance 2li on graph 2|), see Fig. 3. In other words, by the time the rear edge 33 of coil 3| starts to move into the eld a pair of opposed induc- 23 of coil 2| starts into of the length r the longitudinal axis of the rail. I

longitudinal of distortion and starts to generate an opposed F., the said coil 3| has generated an E. M. F. corresponding to the difference in field intensity indicated by the distance 2B. It does not matter how much longer than one-half the distorted iield the horizontal portion 32 of the'- coil is made. for it will be seen that no matter how great said dimension, the full differential represented by 5 distance 26 will be obtained before the rear vertical portion 33 enters the region of flaw. It is the minimum longitudinal dimension of the coil, therefore, which isvimportant and this minimum may therefore be defined as follows:

, Assuming that the smallest sized ssure which the mechanism is designed to detect will yield a distortion longitudinal of the rail of a given d1- mension, then the dimension of the coil longi-r tudinal of the rail should be not less tha-n onehalf of the said distortion. Thus, for instance,

if the mechanism is designed to pick up no smaller fissures than 10% ssures, it is known that the distortion of the eld longitudinal of the rail willv be about 21/2 inches, and therefore the horizontal dimension of coils i5 and i6 corresponding to horizontal portion 32 would be made not less than 11/4 inches. Preferably, however, the horizontal dimension should be made longer than this minimum, since by so doing none-of the advantages 25 are lost while'there is gained the added advantage that there results the maximum eiciency Iin detecting large sized fissures. In such case the horizontal dimension longitudinally of the rail of coils l5 and I6 will be made not less than three inches since the region of distortion caused by a 40% fissure extends for a distance longitudinally of the rail equal to about six inches. In other cases it may be desired to employ coils which are designed to give the maximum output on average fissures which yield a-distortion longitudinal of the rail of about four inches, in which case the longitudinal dimension of the coils I5 and i6 would be made notless than 2 inches.

As hereinbefore stated, the coils J5 and I6 are made at so as to lie close to the rail-head. The reason for this may be seen in diagrams, Figs. 4 and 5. In Fig. 4 it will be noted that the regions iJ-I and i-2 above the rail-head are aiected only by ux in the rail-head, but in the regions 2-3 and 3-5 and beyond, flux lines from the railA web and from the base are encountered and various defects or irregularities due to their construction may eiect said elds. Thus, for instance, spikes and tie-plates may readily affect regions 3--8 while irregularities in the web may aifect regions 2 3. By\forming the coils with short vertical dimension so that they lie close to the rail-head, it will be seen that they avoid ux lines emanating in the web and 'base and thus respond only to variations-of flux in the railhead. s

A further advantage of this construction can be seen by reference to Fig. 5 which is a. graph plotting ux density against distance above the rail. From this graph it will be seen that for equal vertical distances above the rail there is a much greater diiferential close to .the rail-head than inthe regions further away. Thus, in the region lli-i there is a much greater diierence in/ density than in the region I-2, which in turn is greater than the dierence in density in the region 2 3. BY placing the longer coil in the region close to the rail-head; advantage is thus taken of the large -ilux density differentials which take place in said region and therefore the large lvariations in ux caused by the presence of ssures. A

y Thus by constructing acoil which is of predetcrmined length longitudinal of the rail, and causing the height of said coil to be made as small as possible, there results a coil which is rectangular in shape and considerably longer than its height. Such a coil yields the maximum4 output in response to a flaw with a minimum interference from outside causes. v 6

In accordance with the provisions of the` patent statutes, I have herein described the principle and operation ofvmy invention, together with the Vapparatus which I now consider to represent the best embodiment thereof, but I desire to'ghave it 10 understood that the apparatus shown only illustrative and that the invention can be carried out by other equivalent means. Also, while it i's 4designed to use the various featuresand elements in the combination and relations described, some 15 of these may be altered and others omitted without interfering with the more general results outlined, yand the invention extends to such use. Having ,described my invention, what I claim and desire to secure by Letters Patent is: 20 1. In a flaw detector mechanism for rails and than one-half of the field distortion longitudinal 30 y the rail so as to establish an electromagnetic eld 35. I

longitudinal axis of the rail, said coil extending 40 3. In a aw detector mechanism for rails and the like having means for electrically energizing tending longitudinally of the rail for a distance substantially equal to one-half ofthe eld dis- 55 tortion longitudinal of the rail caused by the presence of the average internal defect which the mechanism-is adapted to detect. 4

4. In a aw detector mechanism for rails and thellike having means for electrically energizing 60 nism for detecting variations in said field, said mechanism comprising acoil having its axis'positioned horizontally and transverse with respect 65 to the longitudinal axis of the rau, said coil extending Alongitudinally of the rail for a, distance greater than one-half of the field'distor'tion longitudinal of the rail caused by the presence of the smallest internal defect which it is desired to detect, the portion of said coil extending ina direction normal to the rail being.- shorter than the portion of the coil extending longitudinally of the rail.

5. In a aw detector mechanism for rails and 75 the like having means for electrically energizing the rail so as to establish an electromagnetic field surrounding the same and a detector mechanism for detecting variations in said iield, said mechanism comprising a coil having its axis positioned horizontally and transverse with respect to the longitudinal axis of the rail, said coil extending longitudinally of the rail for a distance substantially equal to one-half of the field distortion longitudinal of the rail caused by the presence of the largest internal defect which the mechanism is adapted to detect, the portion of said coil extending in a direction normal to the the rail so as to 'the mechanism is adapted rail being shorter Vthan the portion of the coil extending longitudinally o f the rail.

6. In a flaw detector mechanism for rails and the like having means for electrically energizing establish an electromagnetic iield surrounding the same and a detector mechanism for detecting variations in said field, said mechanism comprising a coil having its axis positioned horizontally and transverse with respect to the longitudinal axis of the rail, said coil extending longitudinally of the rail for a distance substantially equal to one-half of the eld distortion longitudinal of the rail caused by the presence of the average internal defect which to detect, the portion of said coil extending in a direction 'normal to the rail being shorter than the portion of the coil extending longitudinally of the rail.

'1. In a iiaw detectormechanism for rails and the like having means for electrically energizing the rail so as to establish an electromagnetic field surrounding the same and a detector mechanism for detecting lvariations in said fleld, said mechanism comprising a coil having its axis positioned horizontally and' transverse with respect to the longitudinal axis of the rail, the

portion of said coil extending in a direction nor mal to the rail being shorter than the portion of 'the coil extending longitudinally of the rail.

8. In ailaw detector mechanism for rails and the like having means for electrically energizing the rail so as to establish an -electromagnetic eld surrounding the same and a detector mechanism fordetectlng variations in said ileld, saidA mechanism comprising a substantiallyrectangular coil having its axis positioned horizontally and axis of the rail,. the vertical portions of said coil being shorter than the horizontal portions thereof.

9. In a flaw detector mechanism for rails and the like having means for electrically energizing y the rail so as to establish an electromagnetic Y 'the like having the rail so as defect which itis desired'to detect.

field surrounding the same and a detector mechanism for detecting variations in said neld, said mechanism comprising a substantially rectangular coil having its axis positioned horizontally and transverse Lwith respect to the longitudinal axis of the rail, said coil extending longitudinally of the rail for a distance greater than one-half of therleld distortion longitudinal -oifthe rail .caused by the presence of thej smallest internal 10. Ina flaw detector mechanism for rails and means for electrically energizing to establish an electromagnetic field surrounding the same and a detector mechanism for detecting variations insaid field, said mechanism comprising a substantially rectanthe like having means for electrically energizing lto lie wholly within transverse with respect to'thelongitudinal gular coil having its axis positioned horizontally and transverse with respect to the longitudinal axis of the rail, said lcoil extending longitudinally of the rail for a distance substantially equal to one-half of the of the rail caused by the presence of the largest internal defect which the mechanism is adapted to detect.

11. In a flaw detector mechanism for rails and the rail so as to establish an electromagnetic iield surrounding the same and a detector mechanism for detecting variations in said iield, said mechanism comprising a substantially rectangular coil having its axis positioned horizontally and transverse with respect tothe longitudinalV axis of the rail, said coil extending longitudinally of the rail for a distance substantially equal to one-half of the eld distortion longitudinal of the rail caused by the presence of the average internal defect which the mechanism is adapted to detect.

l2. In a flaw detector mechanism for rails and the like having means for electrically energizing the rail so as to establishan electromagnetic eld surrounding the same and a detector mechanism for detecting variations in said eld, said mechanism comprising a substantially rectangular coil having its axis positioned horizontally and transverse with respect to the longitudinal axis of the rail, said coil extending longitudinally of the rail for a. distance greater than one-half oi.' the iield distortion longitudinal of the rail caused by the presence of the smallest internal defect which it is desired to detect, the vertical portions of said coil beng'sufciently short so as vaxis of the rail, said coil extending longitudinally of the rail fora distance substantially equal to one-half of the iield distortion longitudinal of the rail caused by the presence of the largest internal defect which the mechanism is adapted to detect, the vertical portions of said coil being sufficiently short so as to lie wholly withinY the eld affected only by the rail-head.

14. In -a flaw detector mechanism for rails and the like having means for electrically energizing the rail so as to establish an electromagnetic iield surrounding the same anda detector mechanism for detecting variations in mechanism comprising a substantially rectangular coil having its axis positioned horizontally and transverse with respect to the longitudinal axis of the rail, said coil extending longitudinally of the rail for a distance substantially equal to onehalf of the field distortionlongitudinal of V,the rail caused; by the presence ternal defect which the mechanism is adapted to detect, the vertical portions of said coil being Y suiliciently short so as to lie wholly within the eld aected only by the rail-head.

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field distortion longitudinal 6 the eld affected only by said'ileld. said A of the average in- 

